The present invention relates to an Sb—Te base alloy sinter sputtering target containing carbon or boron and capable of effectively inhibiting the generation of particles.
In recent years, a thin film formed from an Sb—Te base material is being used as a phase change recording material; that is, as a medium for recording information by using phase transformation. As a method of forming this thin film formed from the Sb—Te base alloy material, it is standard to use a means generally referred to as a physical vapor deposition method such as the vacuum deposition method or the sputtering method. In particular, the thin film is often formed using the magnetron sputtering method from the perspective of operability and film stability.
Formation of films by way of the sputtering method is performed by physically colliding positive ions such as Ar ions to a target disposed on a cathode, using that collision energy to discharge materials configuring the target, and laminating a film having roughly the same composition as the target material on the opposite anode-side substrate.
The coating method based on the sputtering method is characterized in that it is possible to form films of various thicknesses; for instance, from a thin film of angstrom units to a thick film of several ten μm, with a stable deposition speed by adjusting the processing time, power supply and the like.
When forming a film formed from an Sb—Te base alloy material for use in a phase change recording film, specific problems arise including the generation of particles during sputtering or the generation of nodules (projections) that cause abnormal discharges (micro arcing) or the formation of clustered thin films (i.e., thin films in which nodules are solidified and attached), the generation of cracks or fractures in the target during the sputtering process, and the absorption of large amounts of gas components such as oxygen during the production process of sintered powder for use in a target.
These problems encountered in targets and during the sputtering process will become a significant cause of deteriorating the quality of the thin film as the recording medium.
It is known that the foregoing problems are largely affected by the grain size of the sintering powder or the target structure or shape. Nevertheless, since the target obtained by sintering is unable to retain sufficient characteristics upon producing an Sb—Te base alloy sputtering target for forming a phase change recording layer, it was not conventionally possible to avoid the generation of particles, abnormal discharge and nodules during the sputtering process, the generation of cracks or fractures in the target during the sputtering process, and the inclusion of large amounts of gas components such as oxygen contained in the target.
As a conventional method of producing an Sb—Te base sputtering target, disclosed is a production method of a Ge—Sb—Te base sputtering target, which is to prepare quenched powders of Ge—Te alloy and Sb—Te alloy by using the inert gas atomization technique, evenly mix the alloys having a Ge/Te ratio of 1/1 and a Sb/Te ratio between 0.5 to 2.0, and thereafter perform pressure sintering (for instance, refer to Patent Document 1).
In addition, disclosed are a production method of a Ge—Sb—Te base sputtering target wherein the oxygen content of a sintered compact, obtained by pouring the powder of which the tap density (relative density) is 50% or higher among various alloy powders containing Ge, Sb and Te into a mold, performing cold or hot pressurization thereto, and sintering a molding material of which the density after the cold pressurization is 95% or higher via heat treatment in an Ar or vacuum atmosphere, is 700 ppm or less; and a technology pertaining to a method of producing powder to be used therein by the atomization technique (for instance, refer to Patent Document 2).
In addition, disclosed is a production method of a Ge—Sb—Te base sputtering target material, which is to prepare quenched powder of a raw material containing Ge, Sb and Te by using the inert gas atomization technique, use the powder of which the grain size is 20 μm or greater and the specific surface area per unit weight is 300 mm2/g or less to perform cold or hot pressure molding, and sinter the compact obtained by such molding (for instance, refer to Patent Document 3).
As other technologies of producing a target using atomized powder, there are the following Patent Documents 4, 5, and 6.
Nevertheless, in the foregoing Patent Documents, the atomized powder is used as is. It is not possible to obtain a sufficient strength of the target, and it cannot be said that the miniaturization and homogenization of the target structure have been achieved. In addition, the tolerable oxygen content is high, and there is a problem in that it is insufficient as an Sb—Te base sputtering target for forming a phase change recording layer.
Moreover, there is also known a sputtering target for forming an optical disk recording film, in which the surface oxide film or the processing layer is eliminated and the average centerline roughness as the surface roughness is Ra≦1.0 μm (refer to Patent Document 7). The object of this target is to shorten the pre-sputtering time or to eliminate the pre-sputtering process entirely, and this method is extremely effective for achieving this object.
Nevertheless, with recent DVDs and BDs (Blu-ray Discs), even higher densification is being achieved, and, in order to improve the production yield, it is extremely important to reduce the particles caused by the target.
Accordingly, as well as the shortening of the pre-sputtering process, it is necessary to improve not only the quality of the target surface but the quality of the overall target in order to effectively inhibit the generation of particles, abnormal discharge and nodules, and the generation of cracks or fractures in the target.
Moreover, recently there have been proposals of reducing the load on the circuit by increasing the electrical resistance of the phase change recording film, reducing the current value flowing during the writing and erasing operation, and reducing the power consumption. As one such method, a proposal has been made for mixing carbon powder into the sputtering target to achieve low resistance (refer to Patent Document 8). However, since carbon powder is nonmetal, if carbon is mixed into a conventional Sb—Te base alloy sputtering target, it rather becomes an addition of foreign matter. There has been a problem that carbon is not necessarily a favorable additive because this easily generates abnormal discharge during the sputtering process, the generation of particles increases, and cracks sometimes occur in the target.    [Patent Document 1] Japanese Patent Laid-Open Publication No. 2000-265262    [Patent Document 2] Japanese Patent Laid-Open Publication No. 2001-98366    [Patent Document 3] Japanese Patent Laid-Open Publication No. 2001-123266    [Patent Document 4] Japanese Patent Laid-Open Publication No. S10-81962    [Patent Document 5] Japanese Patent Laid-Open Publication No. 2001-123267    [Patent Document 6] Japanese Patent Laid-Open Publication No. 2000-129316    [Patent Document 7] Japanese Patent Laid-Open Publication No. 2000-169960    [Patent Document 8] Japanese Patent Laid-Open Publication No. 2004-363541